Brachylophosaurus meaning "short-crested lizard" was a mid-sized member of the hadrosaurid family of dinosaurs. It is known from several skeletons and bonebed material from the Judith River Formation of Montana and the Oldman Formation of Alberta, living about 76.5 million years ago.

This animal is notable for its bony crest, which forms a flat, paddle-like plate over the top of the skull. Some individuals had crests that covered nearly the entire skull roof, while others had shorter, narrower crests. Some researchers have suggested it was used for pushing contests, but it may not have been strong enough for this. Other notable features are the unusually long forelimbs and the beak of the upper jaw being wider than other contemporary hadrosaurs.

Apart from the above, Brachylophosaurus was a typical hadrosaur which reached an adult length of 9 meters (30 ft). Like other hadrosaurs, Brachylophosaurus possessed features like cheeks to keep fodder in the mouth and dental batteries consisting of hundreds of teeth. These teeth could be used to chew efficiently, a feature rare among reptiles, but common among ornithischian dinosaurs like Brachylophosaurus.

In 2003, evidence of tumors, including hemangiomas, desmoplastic fibroma, metastatic cancer, and osteoblastoma was discovered in fossilized Brachylophosaurus skeletons. Rothschild et al. tested dinosaur vertebrae for tumors using computerised tomography and fluoroscope screening. Several other hadrosaurids, including Edmontosaurus, Gilmoreosaurus, and Bactrosaurus, also tested positive. Although more than 10,000 fossils were examined in this manner, the tumors were limited to Brachylophosaurus and closely-related genera. The tumors may have been caused by environmental factors or genetic propensity.

Only three complete fossils of the hadrosaur, or duck-billed dinosaur, Brachylophosaurus have ever been found, but they're so amazingly well-preserved that (as paleontologists often do) they were immediately given nicknames: Elvis, Leonardo and Roberta. (The same research team also found a fourth, incomplete fossil of a juvenile, which they dubbed Peanut.)

Although it's named for the unusually short crest on its head (short, that is, for a hadrosaur), Brachylophosaurus stood out more for its thick, downward-turning beak, which some paleontologists take as evidence that the males of this genus head-butted one another for the attention of females.

The most completely preserved Brachylophosaurus specimen, Leonardo, has been the subject of a 2008 Discovery Channel documentary, Secrets of the Dinosaur Mummy. Here, it's revealed that Leonardo had a birdlike crop on its neck (presumably to aid in digestion) as well as different-sized scales on different parts of its body, among other unique anatomical features. Especially a bite mark left behind from a predatory Tyrannosaur called Daspletosaurus.